An autopsy has been carried out on democracy activist Li Wangyang against his family's wishes.

Li died in a hospital in Shaoyang, Hunan, on Wednesday. Authorities' claims that he hung himself have been widely challenged.

In Hong Kong, at least five more deputies to the National People's Congress (NPC) and China's top political advisory body promised to urge Beijing to investigate Li's death.

By 7pm yesterday, 4,390 mainland and overseas supporters had signed an online petition calling for a proper investigation.

A friend of Li's, who did not want to be named, said he had met Li's sister, Li Wangling, yesterday afternoon and was told the autopsy had already been carried out in the presence of a professor from Sun Yat-sen University in Guangzhou.

'She cried and said her brother had already been opened up, and that she was heartbroken.'

The friend said he had met Li's sister and her husband in a hotel but community officers were present.

The police told Li Wangling earlier that the autopsy would be carried out whether or not she agreed to it.

The family said on Thursday that an autopsy was unacceptable unless conducted by an organisation from outside Shaoyang, and in the presence of the family and a lawyer.

Li - a veteran June 4 activist who served two jail terms totalling 21 years in jail - was deaf and blind when released from prison in May last year.

Supporters believe it would have been impossible for him to have acquired the bandages and tied the noose.

His death prompted rights activist Hu Jia to launch an 'I will not suicide' campaign among dissidents on Twitter and urge the public not to believe it if authorities ever claimed they had taken their own lives.

In Hong Kong, NPC deputies Dr Raymond Ho Chung-tai and Miriam Lau Kin-yee said they planned to ask Beijing to investigate Li's death. That vow was echoed by three delegates to the Chinese People's Political Consultative Conference (CPPCC): Chan Wing-kee, James Tien Pei-chun and Lew Mon-hung. Lew said he could not believe Li killed himself.

'The central government needs to find out the truth ... and if it was murder, [the culprit] has to be strictly punished,' he said.

'If a man can be killed at will for the sake of maintaining stability, what else can we say about genuine human rights?'

Executive councillor Professor Anthony Cheung Bing-leung said the deputies were right to call for truth 'because our society is very concerned about human rights'.

Ho said it had affected the country's reputation on the international stage. The city's delegates will meet next month, and he will consider asking them to discuss the issue.

NPC delegate Lau said she would demand an investigation into Li's death and publication of the findings. Tien, a CPPCC member and the Liberal Party's honorary chairman, will cosign the letter.

But Ip Kwok-him - lawmaker for the Democratic Alliance for the Betterment and Progress of Hong Kong and an NPC delegate - said his party had no plan to weigh into the issue.

'The case has entered judicial procedure on the mainland and we will need to respect the laws of the country,' Ip said. He agreed it was reasonable for Li's family to ask for an autopsy in the presence of a lawyer.

Another NPC deputy, Michael Tien Puk-sun, said he had written to the secretary-general of the NPC Standing Committee, Li Jianguo , asking for an inquiry into Li's death.